The overall goal of this project remains unchanged: It is to study the biochemical factors that regulate anticancer therapy-induced pulmonary fibrosis. We will continue to focus on the bleomycin (BLM) class of antitumor agents and specifically we will study the role of bleomycin hydrolase (BH) in protecting lungs against this agent. We believe this fundamental biochemical information will improve the usefulness of BLM, will help define the pharmacogenetics of BLM-induced pulmonary fibrosis, and ultimately may provide the basis for the generation of less toxic analogs. In addition we expect the structural information obtained on BH will reveal more about the normal function of this cathepsin H-like enzyme. Pulmonary fibrosis is the major dose-limiting toxicity of BLM and we have hypothesized that the sensitivity of lungs is directly related to low levels of the inactivating enzyme BH, which appears to protect other normal tissues. Murine strain differences in pulmonary sensitivity to BLM are now well established but the factors that determine BH expression are not known. Damage to the pulmonary endothelium appears to be an early and essential event in fibrosis and we have hypothesized that BH levels in the pulmonary endothelium are a critical factor determining pulmonary sensitivity. During the next funding period, we propose to complete our analysis of rabbit BH cDNA and then to apply this information to study BH in our murine models. We will capitalize on important reagents that have been developed by us during the last funding period. The Specific Aims are to: 1) clone and sequence rabbit and murine cDNA for BH from nonmalignant tissues, 2) clone and sequence murine genomic BH, 3) analyze the regulation of BH expression, 4) determine the cellular localization of BH in the lungs, and 5) examine the protective role of BH in pulmonary endothelium.